Weeds may help map human brain

How stress affects plant has implications for mental diseases


They're attacked by bugs, left to freeze in the cold, die of thirst in the heat and drown in heavy rains.

Plants lead stressful lives, but how they deal with that stress is little understood.

That's where Frank Turano comes in.

Turano, a molecular biologist at the Agricultural Research Service's Beltsville lab, has spent four years dropping weights on plants, exposing them to extreme temperatures, touching them and grinding up their leaves to study their chemical changes under stress.

"Plants can't move. They can't run away when stress is introduced, so the question is, `How do they deal with the stress in their lives?' " says Turano, who will discuss his work this weekend at a national scientific convention in Baltimore.

His research is aimed at coming up with more stress-tolerant, genetically engineered plants. Crops that grow without pesticides. Flowers that need less water. Lawn grass that won't turn brown.

But experts say that understanding a plant's signaling system could someday also help with research on drugs being developed to treat Alzheimer's disease and other ailments.

Plants react to stress in different ways on the outside.

The prickly pear, for instance, releases a natural antifreeze to deal with the cold and the ocotilla, a Southwestern cactus-like bush, shuts down completely, dropping all its leaves during dry spells, only to rejuvenate when it rains.

But Turano believes that internally plants react to stress the same way as humans, using the same enzymes to send out electrical signals emitting cell-to-cell "911 calls" that warn the plant to put up its defenses.

He's spent the past four years trying to prove that.

Turano's "lab rat" is the arabidopsis, a finger-sized cloverlike weed chosen because it grows to full size within six to eight weeks and is small enough to grow by the hundreds in bread-loaf sized lab trays.

"It's more or less an industry standard," said Turano, 40, who lives in Baltimore.

Turano began his work in 1995 with experiments in which he and a team of assistants touched 60 arabidopsis plants and crushed their leaves at intervals ranging from one to 15 minutes.

He then measured the amounts of two amino acids he believes are keys to the plant's stress signaling system -- glutamate and gamma-aminobutyric acid, or GABA -- that were in the crushed leaves.

His studies showed that, when the amount of stress increased, the levels of GABA shot up while glutamate levels dropped. The levels of both fluctuated in proportion to the frequency of the touching, he said.

Turano said the results didn't surprise him. Scientists have known for 20 years that GABA and glutamate are produced in plants under stress.

But his work is aimed at understanding how and why that happens.

"If we can decipher the pathways that plants use to sense stress, we may understand how some plants survive certain exposures to stress and others don't," said Turano, who is assigned to ARS's Climate Stress Lab.

Turano acknowledges that he has yet to prove his theories. That's at least two years away, with more genetic testing needed on plants, he said.

"There's a lot of circumstantial evidence to support this, but there's no direct link yet," Turano said.

Turano will discuss his work this weekend at this year's annual convention of the American Society of Plant Physiologists, held today until Monday at the Baltimore Convention Center.

Eric D. Benner, a research scientist at New York University's biology department who has worked on plant stress, said Turano's work might have implications beyond the plant world.

In humans, glutamate -- one of the amino acids that triggers the signaling process in plants -- acts as a chemical messenger in the brain, playing a role in how memory is stored. But when they go haywire, glutamates also contribute to mental problems, Benner said.

Faulty glutamate signaling has been linked to Alzheimer's disease, while glutamate overload has turned up in the brains examined post mortem of schizophrenics, he said.

Understanding how glutamate works could lead to using plants as test subjects in the research into Alzheimer's disease, schizophrenia and other mental health problems, he said.

Pub Date: 7/24/99

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